2012/2/3 Ertugrul Söylemez <es at ertes.de>:
> Hello there,
>> I'm trying to build a server for testing the conduit and network-conduit
> packages. As a contrived example the goal is to pick the first three
> lines from the client and send them back without the line feeds. After
> that, I'd like to switch to a simple echo server. This is the code:
>> module Main where
>> import Data.Conduit
> import Data.Conduit.Binary as Cb
> import Data.Conduit.List as Cl
> import Data.Conduit.Network
>> handleClient :: Application
> handleClient src snk =
> src $$ do
> (Cb.lines =$= Cl.isolate 3) =$ snk
> snk
>> main :: IO ()
> main = runTCPServer (ServerSettings 4000 Nothing) handleClient
>> I'm not sure whether it is correct to use the 'snk' sink multiple times,
> and intuitively I'd say that this is wrong. What would be the proper
> way to do this?
>>> Greets,
> Ertugrul
In this particular case, it will work due to the implementation of
snk. In general, however, you're correct: you should not use the same
sink twice.
I haven't thought about it much yet, but my initial recommendation
would be to create a new Conduit using SequencedSink, which takes the
three lines and then switches over to a passthrough conduit. The
result looks like this:
module Main where
import Data.Conduit
import Data.Conduit.Binary as Cb
import Data.Conduit.List as Cl
import Data.Conduit.Network
handleClient :: Application
handleClient src snk = src $$ myConduit =$ snk
main :: IO ()
main = runTCPServer (ServerSettings 4000 Nothing) handleClient
myConduit =
sequenceSink 3 go
where
go 0 = return $ StartConduit $ Cl.map id
go count = do
mx <- Cb.lines =$ Cl.head
case mx of
Nothing -> return Stop
Just x -> return $ Emit (count - 1) [x]
Michael